Several types of conventional and well-known therapeutic treatments for cancer in humans are in common use. These treatments include surgery, X-rays, radiation from radioactive sources, and chemotherapy, and are often combined in various ways to enhance treatment effectiveness.
Although such conventional treatment techniques have been successful in treating cancer in many patients and in prolonging the lives of many other patients, they are frequently ineffective against certain types of cancer and often have severe adverse side effects at the necessary treatment levels. Protracted treatment of cancer patients by X-rays or chemotherapy, as an illustration, tends to eventually destroy or inhibit the patients' natural immunological systems to an extent that many patients eventually succumb to common infectious diseases, such as influenza or pneumonia, which otherwise probably would not be fatal. Also, many patients having advanced stages of cancer or complications may become too weak to withstand the trauma of surgical or other cancer treatments; hence, the treatments cannot be undertaken or must be discontinued.
Due both to the prevalence and the typically severe consequences of human cancer, as well as frequent ineffectiveness of current treatments such as those mentioned above, medical researchers are continually experimenting in an attempt to discover and develop improved or alternative treatment methods for cancer.
Hyperthermia is the generation of artificially elevated body temperatures, and has received serious scientific consideration as an alternative cancer treatment. For instance, much research has been conducted into the effectiveness of hyperthermia alone or in combination with other treatment methods, and the promising results indicate that hyperthermia techniques appear to have the potential for being extremely effective in the treatment of many or most types of human cancers and without the often severely adverse side effects associated with current cancer treatments. Hyperthermia is sometimes called thermal therapy to indicate the raising of the temperature of a region of the body.
Researchers into hyperthermia treatment of cancer have reported that many types of malignant growths in humans can be thermally destroyed, usually with no serious adverse side effects, by heating the malignancies to temperatures slightly below that injurious to most normal, healthy cells. Furthermore, other types of malignant cell masses have reportedly been found to have substantially lower heat transfer to lessen the ability to dissipate heat, presumably due to poorer vascularity and reduced blood flow characteristics. These types of growths appear capable of preferential hyperthermia treatment since the vascularly-deficient malignant growths can be heated to temperatures several degrees higher than the temperature reached by the immediately surrounding healthy tissue. Consequently, it appears that different hyperthermia treatment protocols may allow hyperthermic treatment of those types of malignant growths which are no more thermally sensitive than normal tissue without destruction of normal cells, as well as the higher temperature, shorter hyperthermia treatment times of the more thermally sensitive types of malignancies which exhibit poor vascularity. This is usually an advantage for important medical reasons.
Researchers have further indicated that, as a consequence of these thermal characteristics of most malignant growths and the thermal sensitivity of normal body cells, hyperthermia temperatures for treatment of human cancer should be carefully limited within a relatively narrow effective and safe temperature range. Hyperthermia is generally provided by temperatures over 40 degrees C. (104 degrees F.). Hyperthermia treatment protocols have historically included temperatures well above 60 degrees C., but in recent years have generally been considered to include temperatures as high as 45 degrees C. (113 degrees F.). However, as there may be portions of a cancerous tumor that will exceed this level, the intent is to attempt to get as much of the tumor region above the 40 degree C. region as possible.
At treatment temperatures above the approximate 45 degrees C. (113 degrees F.), thermal damage to most types of normal cells is routinely observed if the time duration exceeds 30 to 60 minutes; thus, great care must be taken not to exceed these temperatures in healthy tissue for a prolonged period of time. Exposure duration at any elevated temperature is, of course, an important factor in establishing the extent of thermal damage to healthy tissue. However, if large or critical regions of the human body are heated into, or above, the 45 degree C. range for even relatively short times, normal tissue injury may be expected to result.
Historically, late in the last century alternating electric currents at frequencies above about 10 KHz were found to penetrate and cause heating in biological tissue. As a result, high frequency electric currents, usually in the megahertz frequency range, have since been widely used for therapeutic treatment of such common bodily disorders as infected tissue and muscle injuries. Early in this century, the name “diathermy” was given to this electromagnetic radiation (EMR) tissue heating technique, and several discrete EMR frequencies in the megahertz range have subsequently been allocated specifically for diathermy use in this country by the Federal Communications Commission (FCC).
The ability to do heat pattern steering permits energy to be focused and directed more selectively to the target tumor region. In order to provide sufficient heat energy to deep-seated target tumors, a lower frequency must be selected. This is because the penetration attenuation of human tissue increases at higher frequencies. As frequency is lowered however, the heating focus diameter increases. Thus, the proper frequency is needed to provide the optimum depth within acceptable heating pattern size limits. In general, hyperthermia is best applied when target tissue around the diseased area is also heated. This provides preheating of inflowing blood and reduces thermal conduction from the perimeter of the tumor to draw heat out of the tumor perimeter.
Current systems for applying electromagnetic radiation (EMR) to targets, such as living bodies and biological tissue, and for controlling the position of a region of heating within the target, typically include a plurality of electromagnetic radiation applicators powered by a multi-channel EMR system to provide heat pattern steering control through electronic phase and power steering. However, both the power and phase of the radiation output generated by each applicator must be controlled by a separate power channel of the EMR system to create the desired phased-array steering of heat pattern. Thus, an independent and individually-controllable power signal channel for each electromagnetic applicator is needed, which results in high system complexity and cost. Typically current systems require 4 or 12 independent EMR power signal channels to provide such electronic steering.
Some advanced hyperthermia EMR systems utilize multi-channel phased array systems that control frequency as well as the radiated power and relative phase. Each channel has electronic controls of power and phase and is connected to different antennas. The application of complex and expensive multi-channel amplifier systems to provide multiple EMR synchronous phase energy channels that have phase control to steer the heating region in the body allows electronic steering of the heating pattern, but at high cost and complexity which can make the treatment system cost prohibitive for routine clinical use.
Thus, there exists need for EMR applicator apparatus, and corresponding methods for EMR irradiation, which provide simplified heat pattern steering of EMR heating in a target, such as a target of biological tissue in a living body or tissue simulating matter.